In late 1981, Gottlieb et al described an apparently new immunodeficiency syndrome in homosexual men living in the United States. We now know the syndrome as AIDS (Acquired Immune Deficiency Syndrome), recognize the retrovirus HIV (Human Immunodeficiency Virus) as its cause, and describe the involved cell subset as CD4-positive (CD4+) T cells. The absolute count of CD4+ T cells in peripheral blood was quickly identified as a valuable prognostic measurement in HIV-infected patients. AIDS originated in Africa, and it is there, and in other resource-poor areas of the world, that the disease has had the greatest impact on public health. Since effective antiretroviral therapy (ART) became available in the developed world in the 1990s, the United Nations, various governments, and nongovernmental organizations such as the Gates and Clinton Foundations, have sought to provide affordable treatment to at least some of the millions of HIV-infected adults and children in resource-poor countries in Africa, Asia, the Caribbean, Eastern Europe, and South America. Optimal planning and monitoring of such therapy would be facilitated if equally affordable CD4 counting technology were available. Flow cytometry is recognized as the "gold standard" for CD4 counting in affluent countries, in which several million tests are performed annually at a cost of tens of US dollars each. In resource-poor areas, an "affordable" CD4 counting test means that test must cost no more than a few dollars, and be usable in areas without the infrastructure typically required to support complex diagnostic apparatus such as flow cytometers. The measurement capabilities required to do CD4 counting can now be incorporated into substantially smaller, simpler, more energy- efficient, less expensive devices without any loss of accuracy and precision. This project will determine the minimal instrument configuration for a two-parameter low-resolution fluorescence imaging cytometer using light-emitting diodes (LEDs) for fluorescence excitation and a CCD (charge-coupled device) or CMOS (complementary metal oxide semiconductor) camera chip(s) for photodetection, suitable for CD4 counting using fluorescently labeled monoclonal antibodies, and requiring only minimal sample handling and operator training. It will also be determined whether combinations of antibodies bearing a single fluorescent label can be used to accurately identify CD4+ T cells and other lymphocyte subsets in a single-parameter fluorescence imaging or flow cytometer. AIDS (Acquired Immune Deficiency Syndrome) affects millions of adults and children worldwide, and it is in resource-poor areas of the world that the disease has had the greatest impact on public health. Various government and nongovernmental agencies have sought to provide affordable antiretroviral therapy (ART) to some of the millions of HIV-infected adults and children. Optimal planning and monitoring of therapy would be greatly facilitated by an affordable CD4 counting technology. This project will attempt to produce a simple, rugged, extremely inexpensive automated CD4 counting device using light-emitting diodes and digital camera and computer technology, and requiring only minimal sample handling and operator training. [unreadable] [unreadable] [unreadable]